Electron discharge device



April 16, 1946. A. \`/.`HAEFF i 2,398,499

- ELCTRON DISCHARGE DEVICE Filed May 29, 1941 3 Shvebs-Shec l C 6 S/ 'S2 53 COLL. C G

INVENTOR. ANDREW l/. HAEFF ATTORNEY.

April 16, 1946. Av. HAEFF ELEGTRON DSCHARGE DEVICE Filed May 29, 1941 3 sheets-Sheet 2 INVENTOR. ANDREW V. HAEFF I ATTORNEY.

April 16, 1946. A` V; HAEFF 2,398,499

A ELE'CTRON DISCHARGE DEVICE Fil'ed May 29, 1941 3 Sheets-Sheet 5 Illllllll`- fg NNN INVNTOR. ANREW u HAEFF ATTRNEY.

NRL.-

Patented Apr. 16, 1946 ELECTRON DISCHARGE DEVICE Andrew V. Haeff, Washington, DL C., assignor to `Radio Corporation of America, a corporation of Delaware Application May 29,1941,"seifia1Np. 395,709 p 13 claims. (Cl. 25o-27.5)

My invention relates to electron discharge devices and associated circuits having improved operating characteristics and particularly `suitable for use at ultra-high frequencies.

The present application is a continuation in part of my copending application, Serial No. 375,029 led January 18, 194:1,M and assigned to the same assignee as the present application.

It has been demonstrated that tubes utilizing conventional grids for controllingr current are well adapted for operation at ultra-high frequencies and retain their characteristicadvantage of possessing high transconductance. of the diiiiculties encountered in operating amplifying tubes at ultra-high frequencies is 'the presence of considerable loading in the input circuit which results in an excessive amount of power being required to drive the tube. This decreases the effective power gain of the tube when operated as an amplifier.

The fundamental causes of high input loading are (1) ohrnic and radiation resistance losses due to high circulating currents in electrodes and leads; (2) electron loading which results from the interaction of the electron stream with the circuit, including degenerative or regenerative effects caused by lead impedance.

In order to reduce ohmic resistance losses it is necessary to use internal leads and external conductors made of high conductivity material and having large peripheries. In addition inter-electrode capacitances must be reduced as much as possible in order to minimize circulating currents. To reduce radiation losses a thoroughly shielded circuit of conventional design or closed type cavity resonators must be used.

The principal object of my invention is to pro# vide an electron discharge device and associated circuit having means for substantially reducing or completely neutralizing electron loading when the device is used at ultra-high frequencies.

It is also an object of my invention to provide an electron discharge device having means for minimizing ohmic and radiation resistance losses when the device is used at ultra-high frequen-` cies.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken inconnection with the accompanying drawings in which Figures 1 and 2 are diagrammatic representa- However, one

ures 3 and'` 4; Figures land 8 are diagrammatic representations of tubes and circuits made according to my invention for practicing my invention; Figure 9 is a longitudinal section of an electron discharge device made according to my inventionl and Figure 10 is a longitudinal section of a modil cation of an electron discharge device mad according to my invention.

In order to understand better the effect of e1ec` tron loading, the mechanism of interaction be# tween the electron stream and the electrodes to which circuits may be connected willbe reviewed. Consider a system of twoelectrodes I 0 and II as shown in Figure 1. Assume that electrons travel from the electrode ID, which may be a cathode, to the electrode II, which may be an anode. During electron transit an image charge appears on the electrodes equal in magnitude to the total charge present at any moment within the interelectrode space. The division of the image charge between the two electrodes depends,

tions of electrodes and the movement of electrons between the electrodes; Figures 3 and 4` are diagrammatic representations of conventional tubes and methods of operating the same; Figures f 5 and 6 are curves representing the relationship of the'electron loading (conductance) and the transit time of the electrons of the tubes in Flgin general, upon the instantaneous distribution of charges `moving within the interelectrodef space and upon the coniiguration of` the e1ec` trodes. The current induced in an electrode`due to motion of a charge is'` equal toithe rate of time variation of theA induced image charge on the electrode due tothe moving charge. The total instantaneous current induced in the electrode by theelectron stream will be found bysumming the individual `currents induced by all charges moving within `the interelectrodeV space. If aV voltage exists between electrodes I 0 and II the e displacement current due to the interelectrode capacitance must `be also taken into account.

Consider now a three-electrode system formed,

for example, by a cathode I0, a control grid |2 and the plate II of a triode. Two spaces have to be considered. The total current induced in ,the intermediate electrode I2 (Figure 2) is contributed by moving charges in both spaces, I 0-#I 2 and I 2I I, and the total current is equal to the vector sum of the two currents. The power generated or absorbed by the electron stream within the spaces I 0-I2 and I2-II depends upon the respective current, voltage and the phase angle between'the current and voltage in each space'.

Thus the power generated or absorbed withinethe spaces III-IZ and I2-I I,wi1l be:

when there may exist considerable"penetration of the electric elds from space I Z-I I into space III-I2, one must also .consider direct interaction between electrodes II-IIL so that a power -W1o-1`1'=i1o-11-V1911 Cos into account.'V 1

In order .to reducev the electron loading the pio-.11 also must be taken is a minimum.

In a conventional negative grid tetrode, operated at low frequencies the input electrode loading will be negligibly small if thedriving voltagey is applied in a conventional manner between thev grid and the cathode so that the voltage also appears between the control grid G and theI screen Y S. (See Figure 3.) The R.F. electronic current passing in the G-S space is very nearly equal and opposite in phase tothe current inl the space so. that the vtotal drivingV power lis very,V nearly Zero.

However, ina circuit shownin Figure 4 where the driving-.voltage is applied between the grid and the cathode only, but Adoesnot appear, be,.

tween the grid and the screen, ftheloading vwill be very severe at Ylow frequencies. lThis-loading is due to the fact that even though a current, equal to C- G space current, iiows in'the- G-S space, no voltage is present in this region-and?y hence-no negative power is developedin theA G-S space to balance the power absorbed in -the C-G space.

As -the driving frequency is, increased the `circuit .o-Figure V3 will exhibit ,electronv loading which initially `will increase with the frequency.. Thisloading is'due to the fact that with increasing electron -transittime compared to a period of the applied voltage frequency the amplitudes Vand phases of currents in the C-G and G-S spaces change yin such a mannerv thatthe amounts of powerabsorbed and generated in the two spaces no -longerbalance each other. VFor the case of a high-p control grid whenthe spacings and D.C. voltages are such thatthe G-S electron transit time isnegligible `compared to C-G transit time an analysis-shows that the electron loading '(conductance) will vary with transit time as shown in tFigure 5. Here the ordinates of thefcurve represent the ratio G/Gmo where G=conductance of Ythepgrid `G dueto electron motions` ,and Gmn=transconductance of the Grid G at very low or zero frequency, .that is when thetransittime of the electron is negligible in comparison to the time of one cycle of the frequency of the applied voltage.v The abscissae represent the ratio -r/T that is-thek ratio ofv the transit time of the electron to the period of oscillation of the applied alternating voltage. The electron loading increases rapidly with transit time, reaches a maximum at the value of transittime `v equal to 0.85 Vof the oscillation period T and then, underideal conditions, passes through zero and. becomes negative. In the case of circuit shownin Figure 4 the varitions frequently lie outside the useful operating range of the tube. The tubes could be designed for this optimum condition but, in general, this may .necessitate a compromise, so that high transconductance may be partly sacrificed. The present invention provides means for neutralizing-electron loading for a wide range ci frequencies and operating voltages without any sacrice of the useful characteristics of the tube, such as high transconductance.

' A general scheme is that in addition to the driving voltage applied between the cathode and grid, .a voltage is developed between the control grid and the screen of such a magnitude and phase -as to generate power in the grid-screen space andthis power is fed back into the cathodegrid circuit, so that it will balance the power absorbed in thecathode-grid space.

A schematic diagram of such a circuit is represented in Figure '7. An impedance Z2 is introduced between the screen S and the grid G of such magnitude and phase angle that the current ie-s will produce a voltage V2 across this impedance.`r They power` W2=iesV2 cos (io-sVz) generated in the Gr-S space is then fed to the grid-cathode circuit Z1 by means of a coupling circuit Zo. The impedances Z1 and Z2 Vusually takethe form 4of tuned circuits and the coupling impedance Zu may be the inter-electrode capacivtance or an auxiliary coupling element.

Figure 8 shows schematically the input loading neutralization circuit in combination with an inductive type output circuit. Here the outputY circuit Z is connected between the two screening electrodes S1 and S2. The suppressor and .current collecting electrodes, represented respectively by. S3 and coll., are also shown. In the above circuit diagrams only the essential R.F. circuits are indicated. Blocking, ground- Ving and by-passing condensers which are used for 'providing isolation of electrodes for D. C., so that application Briefly thistube comprises a cathvode for supplying. a beam of electrons and a collector for -receiving the electrons. A modulatingl grid is placed adjacent the cathode for modulating the kbeam of electrons which passes to the collector. Surrounding the beam path is a resonant cavity circuit comprising a hollow member having a passageway extending therethrough through which the beam passes. The passageway is provided with a gap lying in a plane transverse to the beam path. As the modulated beam of electrons passes across this gap, energy ation-of electron loading Ywith transittime will Y be as shown in Figure 6.` Starting with its maxil mum value at low frequency the loading decreases with increasing frequency.

These curves indicate that for certain values of electron transit angle, that is for certain -values ofthe'ratio of L transit time T "g period of oscillation and operating voltages for theseoptimum condiis transferred from the beam to the resonant cavity circuit which provides the output circuit for the tube and which can be coupled to a radiatoror to an amplifier.

Referring to Figure 9, the electron discharge device includes the elongated tubular cathode I0 provided with an emitting coating lll and surrounded successively by concentric electrodes including the control grid ll consisting of longitudinally extending parallel rods secured to a-disc I l'-,-the first screen electrode l2 compris ing a plurality of radially positioned Slat-like electrodeelements and a second screen electrode i3 consisting oli-radially positioned Slat-like elecmember I9 supporting the cathode and surroundv ing the lead `2l). The tubular member I9 is surrounded in turn by the tubular member'22 supporting the grid, the tubular members being capacitatively closed at their free end by means of ring-like member 23 to form a concentric line tank circuit. This concentric line arrangement serves as the input tank circuit between the cathode I and the control grid II.

The output tank circuit is of the resonant cavity type. Extending from the opposite ends of the Slat-like screen electrodes are the tubular members 24, 24 and 25, 25. These concentric and coaxial tubular members are electrically closed at their ends by ring-like members 26 and 26 for providing an output tank circuit.

The control grid-screen grid resonant cavity tank circuit is provided by means of concentric tubular member 21 capacitively coupled with member 25 and closed at the end by ring-like member 28. The other end of the resonant cav-f ity tank circuit connected to the screen grid electrodes is provided with extension 29 between which and member 24 there is a gap, the extension 24 being closed by the transverse disc 30 to form a cup-shaped cavity, the open end of extension 29 being closed by re-entrant insulating portion 3| which also serves as a seal. A tuning condenser in the form of a plunger 32 is provided which can be moved longitudinally of the tubular members 24, 24 across the gap for tuning the output tank circuit. The collector electrode I4 is insulatingly supported with respect to the other electrodes by means of the cupshaped closure member 33 connected between the water jacket of the collector and the leads for the other electrodes and by the collar 34 sealing the water jacket of the collector and the closure member 26 so that the space occupied by the electrodes may be evacuated to provide an evacuated envelope for 'these electrodes.

Coupling between the cathode-control grid circuit (Z1) and control grid-screen grid tank (Zz) may be controlled by means of the coupling loop 35 (Zo). The input is coupled to the cathode grid space by coupling loop 36 and the load coupled to resonant cavity output tank circuit between the screen grid electrodes by means of coupling loop 31.

The cathode heater voltage is supplied by transformer 38 and grid bias by voltage 38', the positive voltage for the collector I5 being supplied by voltage source 39 and for the tank circuit by voltage source 40.

In operation the electrons emitted by the cathode pass through the control grid where they are closed by ring shaped member 64'.

' elements provide the output resonant cavity for modulated and formed into radial beams after which they enter into the space between the screen electrodes where the modulated electrons are subjected to the high frequency iield of the output tank circuit connected to the screen electrodes in suchphase that energy is-extracted from the modulated beams to excite the tank circuit before they are collected by the collector. Coupling exists between the control grid II and rstscre'en electrode I2 so that energy from the screen electrode-control grid space is fed back into the control grid-cathode space, the amount rof `feedback being controlled by means of `the- `lcoupling loop 35, which couples the iield within the cathode-control grid space and the iield in the control grid-screen electrode space. Tuning of the output tank circuit can be accomplished `bymeans of tuning condenser 32. By means of the arrangement disclosed'the desirable characteristics sought are obtained.

It will thus be apparent that by means of the centric lines and resonant cavities used are of high conductivity material and large diameter and due to the eiective by-passing of the radio frequency currents. Radiation losses are reduced to a minimumbecause ofthe shielded circuits. Thus all three objects contemplated by my invention are practiced to provide a tube particularly suitable for use "at ultra-high frequencies at high eiiciencies. f

In Figure 10 is shown a modiiication of the device shown in Figure' 9. The indirectly heated cathode 50 is provided with the `heater coil `5I and is surrounded in turn by control grid 52, rst screen electrode 53, second screen electrode 54 and collector 55, the electrodes being of substantially the same construction as that shown in Figure 9 except for thecollector which is of different form and is provided with the in-take member 56, and outlet member 5'I for permitting circulation of the cooling medium through the collector. The cathode heater and grid electrodes are supplied with leads extending through and sealed into a cup-shaped member 50 and electrically connected to the tubular extensions 58 and l59 which form together a coaxial line input tank circuit, this tank circuit being tuned by' tuning condenser 69 in the form of a collar surrounding vhollow conducting member 58 and movable by means of rod 6I longitudinally of the coaxial line tank circuit. One of the heater leads and conductor 62 lie within the tubular member 58. The screen and accelerating electrodes are provided with tubular extensions`63 and 64, which are concentric and coaxial and are electrically The other ends of the screen and accelerating electrodes are provided with hollow like extensions 63 and 64', to which side walls 65 and 65 having `a resonant cavity tank circuit are connected. The

resonant cavity tank circuit is closed at the outer peripheries of the Wall by ring shaped `member 66.` Thus the screenelectrodes and associated the tube.` Tuning of this resonant cavity is accomplished in substantially the same manner as in the tube shown in Figure 9. An extension 61 is provided spaced by means of a gap from tubular member 63 closedbykmeans of thetransverse disc-like member 68. Extending within the tubular members 6I and 63 is re-entrant portion To provide a screen electrode-control grid resonant cavity a cup-shaped member 'I2 is supported on the tubular members 59 and surrounds and is f coaxial withthe tubular member 59, capacitive coupling existing y between thisy member and- `shielding member 'I3 electrically connected to the lar member 159,; cup-shapedy member 12,v shielding member 13 and wallBBj of the tank circuit and collar 63 electrically connected to the screen grid. Tuning of this resonant cavity is accomplished by member 14 slidable longitudinally ofthe circuit by means of rod 15. Input coupling is provided by means of loop 11 and output is obtained from the tank circuit Yby means of coupling loop 18 mounted within re-entrant insulating seal 19. Heating potentials are applied from voltage source t and biasing potentialsv for the grid by source 80. Potentials for the tank circuit are obtained from voltage source Bland for the collector from voltage source 82.

The tube operates in substantially ther same mannerl as the tubeshownin Figure 9, coupling between the control grid-cathodev circuit and the control grid-screen grid circuit being had by means of coupling loop 16.

It will beapparent from the above discussion and description that I have provided an electron discharge device particularly suitable for use at-.ultra-high frequencies since both ohmic and radiation resistance losses due to high radio frequency circulating currents in electrodes and leads have been substantially eliminated, andbecause electron loading, which re` sults from interaction yof the electron stream and the circuit, including regenerative or degenerative effects caused by lead impedance, has also been substantially neutralized.Y This is accomplished by means of leadsand external conductors of highly conducting material and large diameter. The radiationlosses are reduced to a minimum by thoroughly shielded circuits comprising closed type cavity resonators.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specic application for which my invention may be employed, it will be apparent'V that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variaions may be made in the particular structure used and the purpose for which-it is employed without departing from the scope of my invention as set forth in the` appended claims.

What I claim as new is:

l. An electron discharge device having a cathode electrodefor supplying a stream of electrons and a collector electrode for collecting said electrons and surrounding said cathode, ya control electrode surrounding said cathode and intermediate said cathode electrode and said collector electrode and a screen `electrode surroundingsaid cathode and control `electrodes and intermediate said control electrode and collector electrode, a first impedance including a hollow body forming a resonant .cavity tank circuit connected between said cathode and control electrode; and a second impedance including a hollow'mernber forming a second hollow resonantcavity tank circuit coupled between the control electrode and screen electrode, said electron discharge device having means electrically coupling said tank circuits together.

2. An electron discharge device having a cathode electrode for supplying a streamof electrons and a collector electrodeV surrounding said cathv ode for collecting said electrons, a control electrode'intermediatefsaid cathode electrode and saidcollectorelectrode Vand surrounding-Said cathode, and aY screen electrodexsurrounding said wall ortlieresonant cavity., The Control-grida rst screen grid tank circuit then, comprises -tubucathode andcontrol electrodes` and intermediate said controll electrode `and -collector electrode,V a first impedance including a concentric line tank circuit connected between said cathode and control electrode, and a second impedance including a hollow conducting member forming a resonant cavity tank circuit connected between the control electrode and screen electrode, and means electrically coupling said impedances together, and a second resonant cavity tank circuit intermediate saidv screen electrode and said collector electrode forv inductively extracting energy from the electron stream as it moves from said cathode to said collector.

3. An electron discharge device having a cathode electrodefor supplying a stream of electronsv and a collector electrodersurrounding said cathode for collecting said electrons, a control electrode surrounding saidl cathode electrode and intermediate said cathode electrode and said collector. electrode for modulating said stream of electrons andra pair of successively positioned screen electrodes surrounding said cathode and control electrodes and intermediate said control electrode and collector electrode, a concentric line tank circuit connected between said cathode and control electrode, and a hollow conducting member-electrically coupled betweenthe control electrode and one of said screenelectrodes and forming a resonant cavity tank circuit, said electron discharge device having means electrically coupling said tank circuits, and a resonant cavity tank circuit electrically coupled between said pair of successively positioned screen electrodes and surrounding the path of said electron stream between the control electrode and the collector electrode for inductively abstracting energy from said electron stream'during operation of said electron discharge device.

4. u Al'l electron discharge device having a cathode electrode for supplying a stream of electrons anda collector electrode Surrounding said cathode electrode for collecting said electrons, a control .electrode intermediate said cathode electrode and said collector electrode and surrounding said cathode electrode, and a screen electrode surrounding said cathode electrode andv control electrodes intermediate said control electrode and collector electrode, a tubular member electrically coupled to said cathode electrode, a rst conducting member electrically coupled to said control electrode and coupled to said tubular member and forming with said tubular member a tank circuit, a second conducting member electrically coupled to said screen electrode and coupled to said iirst conducting member and providing with said lirst conducting member a second tank circuit, and coupling means coupling said tank circuits together.

5. Anelectron discharge device having a cathode electrode for Supplying a stream of electrons and a collector electrode surrounding said cathode.. electrode for collecting said electrons, a control electrode surrounding said cathode electrode land intermediate said cathode electrode and said collector electrode, and a pair of successively positioned screen electrodes intermediate said control electrode and collector electrode, a tubular member electrically coupled to said cathode electrode, a second tubular member surrounding said first tubular member and electrically coupled to said control electrode and forming ,withrthev first tubular member a rst tank circuit, a third .tubular member surrounding and electrically coupled to said second tubular member and one of said screen electrodes and providing with said second tubular member a second 'tank circuit, and means coupling said tankcircuits together, and a hollow resonant cavity tank circuit; electrically connected between said screen electrodes.

6. An electron discharge device having a, cathode electrode for supplying a stream of electrons and a collector electrode surrounding said cathode electrode for collectingsaid electrons, a grid electrode surrounding said cathode electrode and intermediate said cathode electrode and said collector electrode, and a pair of successively positioned screen electrodes intermediate said grid and collector electrodes, a rst tubular conducting member electrically coupled to said cathode electrode, ,a second tubular conducting member electrically coupled to said grid and surrounding said rst tubular conducting member and forming therewith a, tank circuit, a third conducting member electrically coupled to one of said screen electrodes and surrounding said second tubular conducting member and providing therewith a second tank circuit, and coupling means coupling said tank circuits together, and concentric tubular members extending from opposite `ends of said screen electrodes and electrically closed at their free ends providing an output resonant cavity for inductively extracting energy from said electron stream as it passes between said cathode and said collector electrode.

'7. An electron discharge device having a cath'- ode electrode for supplying a stream of electrons and a collector electrode surrounding said cathode electrode for collecting said electrons, a control electrode intermediate said cathode electrode and said collector electrode and surrounding said cathode electrode, and a screen electrode` surrounding said cathode electrode and control electrode and intermediate said control electrode and collector electrode, a rst impedance including a concentric line tank circuit connected between said cathode electrode and control electrode, and a second impedance comprising a hollow conducting member forming a resonant cavity tank circuit connected between the control electrode and screen electrode, and means electrically coupling said impedances together, and an output circuit connected to said electron discharge device. Y

8. An electron discharge device having a cathode for supplying a stream of electrons and a collector electrode surrounding said cathode for collecting said electrons, a controlY electrode surrounding said cathode and intermediate said cathode electrode and collector electrode, a pair of successively positioned screen electrodes surrounding said cathode and control electrode and intermediate said control electrode and collector electrode, and an electrically resonant h'ollow body connected between said cathode and control electrode and providing an input circuit and a. hollow conducting member electrically coupled between the control electrode and one of said screen electrodes and forming a, resonant cavity tank circuit, said electron discharge device having means electrically coupling said electrically resonant hollow body and said tank circuit together,

and a resonant cavity tank circuit electrically coupled between said pair of successively positioned screen electrodes for inductively abstracting energy from said electron stream during operation of said electron dischargedevice.

ode electrode for supplying a, stream of electrons and a collector electrode surroundingsaid cathode electrode for collecting said electrons, a, conrst tubular member and electrically coupled to said control electrode and forming with said rst tubular membera tank circuit, a third tubular member surrounding and electricallycoupled to said second tubular member and one of said screen electrodes andproviding withsaid second tubular member a second `tankncircuit, means coupling said tank circuits together, and a hollow resonant cavity tank-circuit electrically coupled betweensaid screen electrodes.

10.,An electron'discharge device having a cathode electrodefor supplying a stream of electrons and a collector electrode surrounding said cathode electrode for collecting the electrons, a grid electrode surrounding said cathode electrode and intermediate-said cathode electrode and said collector electrode for modulating said electron stream! and a pair of successively positioned screen electrodesintermediate said grid electrode and collector electrode, a lrsttubular conducting member electrically coupled to said cathode electrode, a second tubular conducting member electrically coupled to said grid electrode andsurrounding said rst tubular conducting member and forming therewithV a tank circuit, a third conducting member electrically coupled to said screen electrodes and surrounding said second tubular conducting member and providing therewith a second tank circuit and coupling means coupling said tank circuits together, and concentric tubular members extending from opposite ends of said screen electrodes and electrically closed at their free ends for providing an output tank circuit for inductively abstracting energy from the modulated electron stream as it passes between the cathode andsaidcollector electrode, one of said screen electrodes being provided with a cup-shaped element at one end thereof and a tubular extension connected to the other screen electrode registering with said cup-shaped member and separated therefrom by means of a gap, and a tuning plunger movable longitudinally between the cup-shaped member and the tubular extension for tuning the output tank circuit.

1l. An electron discharge device having a cathode electrode for supplying a stream of electrons and a collector electrode surrounding said cathode electrode for collecting the electrons, a grid electrode surrounding said cathode electrode and intermediate said cathode electrode and said collector electrode for modulating said electron stream, and a pair of successively positioned screen electrodes intermediate said grid electrode and collector electrode, a first tubular conducting member electrically coupled to said cathode electrode, a second tubular conducting member electrically coupled to said grid electrode and surrounding said iirst tubular conducting member and forming therewith a tank circuit, a third conducting memb'er electrically coupled to said screen electrode and surrounding said second tubular conducting member and providing therewith a` second tank circuit land cbupling means coupling said tank circuitsV together, one of said screen electrodes being provided with a cup-shaped element at one end thereof and a tubular extension on the other screen electrode registering with said cup-shaped member and separated therefrom by means of a'gap, and a tuning plunger movable longitudinally between the cup-shaped member and the tubular extension, and a radially positioned cavity resonator at the other end of said screen electrodes and having one wall electrically connected to one of said screen electrodes and having another wall electrically connected to the other screen electrode.

l2., An electron discharge device having a cathode electrode for supplying a stream of electrons and a collector electrode surrounding said cathode electrode-for collecting electrons, a grid electrode surrounding said cathode electrode and intermediate said cathode electrode and said collector electrode, and a'pair of successivelypositioned screen electrodes intermediate said grid electrode and collector electrode, a` first conducting member electrically coupled to said cathode `electrode, a tubular conducting lmember Velectrically coupled to said grid electrode and surrounding said first conducting member andV forming therewith a tank circuit, concentric tubular members extending from opposite -ends of said screen electrodes and electrically closed at their free ends for providing an output tank circuit for inductively abstracting energy from the electron stream as it passes between the cathode and said collector electrode, and a-cup-shaped member electrically coupled to one of said screen electrodes and to the grid electrode providing a cavity resonator between the screen electrodes and the grid electrode, and a coupling loop coupling said last resonant cavity with the tank circuit electrically coupled between the grid electrode and the cathode electrode. Y

13. An electron discharge device having a cathode electrode for supplying a stream of electrons and a collector electrode surrounding said cathode electrode for collectin'gthe electrons, a grid electrode surrounding ksaid cathode electrode and intermediate said cathode electrode and said collector electrode for modulating said electron stream, and a pair of successively positioned screen electrodes intermediate said grid electrode and collector electrode, a rstrtubular conducting member electrically coupledV to said cathode electrode, a second tubular conducting member electrically coupledto said grid electrode and surrounding said 'lrst tubular conducting member and forming therewith a tank circuit, a third tubular member electrically coupled to one of said screen electrodes and surrounding said second tubular member and providing therewith a second tank circuit, and coupling means coupling said tank circuits, and a radially positioned cavity resonator at one end of said screen electrodes and having one wall electrically connected to said one screen electrode and the other wall electrically connected to the other screen electrode.

' f ANDREW V. HAEFF. 

